1. Field of Application
The present invention relates to an electrical power supply system (referred to in the following simply as a power supply system) installed in a motor vehicle, for regulating the electrical power produced from an electric generator that is driven by the vehicle engine.
2. Description of Related Art
Due to the increased amount of electrical equipment installed in motor vehicles in recent years, with an accompanying increase in the level of electrical power that must be generated for operating such equipment, it is becoming necessary for the engine-driven electric generator of a vehicle to produce a higher level of electrical power. A correspondingly higher level of torque must be applied by the engine to the electric generator, to effect an increase in electrical power output, and this results in an increase in the engine fuel consumption. It would be desirable to reduce the extent of such increased fuel consumption.
In the prior art, as a technique for reducing engine fuel consumption, the costs of generating electrical power under various operating conditions are calculated, and electrical power generation is concentrated on periods when the cost is low. Such a technique has been proposed for example in Japanese patent publication No. 2004-260908 (pages 8 to 13, FIGS. 1 to 8), referred to in the following as reference document 1.
However with the method described in reference document 1, the variations in the generated electrical power may be greater and occur more frequently than those which occur with a conventional type of voltage regulation, so that the problem arises that the power supply voltage (i.e., which is both the generator output voltage and the voltage of the vehicle battery) may vary rapidly, with large-scale fluctuations. As a result, the power supplied to electrical equipment such as the vehicle headlamps will fluctuate. Problems such as flickering of the headlamps may thereby occur, which can be annoying to the vehicle driver.
Furthermore, due to such large-scale variations in electric generator output power, the level of engine torque that is absorbed by the generator will vary significantly. In particular, when there is a sudden large increase in the torque load on the engine within a short period of time, a substantial lowering of the engine speed may occur. Hence the problem arises that momentary deceleration or acceleration of the vehicle may occur due to changes in the load torque on the engine that result from operations to control the state of charge of the battery to a suitable level, i.e., performed during periods when battery charging can be performed with minimized fuel consumption.
This may cause annoyance to the vehicle driver. In addition, lowering of the engine speed over a long period of time, with insufficient power being thereby produced by the generator, may cause problems with the operation of vehicle equipment.
Furthermore, with prior art types of power supply control apparatus for an electric generator of a vehicle, changes in the load power demand (i.e., amount of power consumed by electrical loads) can result in momentary changes in the power supply voltage, while the resultant variations in the torque load on the engine can result in changes in the engine speed, causing momentary acceleration or deceleration of the vehicle.